The invention relates to a variable mechanical valve control for an internal combustion engine for regulating the control timing, the opening time and/or the stroke of gas exchange valves, intake and exhaust valves, and for actuating fuel valves of an internal combustion engine, particularly of engines having push rod or rocker arm trains.
Known are internal combustion engines with an underhead camshaft, in which a push rod driven by the camshaft or the cams themselves directly actuate(s) a rocker arm, which opens and closes the valve either directly or by way of further transmission members. In this process, however, neither the control timing nor the valve stroke or the valve opening duration is usually varied continuously. If such mechanically variable valve stroke controls have only a camshaft, on which the cams for the intake and exhaust liftings of the valves are provided simultaneously, the time point of the opening and closing of the intake valve cannot be controlled independently of the time point of opening and closing of the exhaust valve. Used in a known way for shifting the opening time points between intake and exhaust valves is a phase shifter, the cam geometries for the intake and exhaust valve stroke being provided on different camshafts. The intake camshaft is then shifted relative to the exhaust camshaft for the phase shifting.
Also known are internal combustion engines with an overhead camshaft, in which a cam driven by a control shaft directly actuates a rocker arm, which, either directly or by way of further transmission members, opens and closes a gas exchange valve. In this process, however, neither the control timing nor the valve stroke or the valve opening duration is varied continuously. If such mechanically variable valve stroke controls have only a control shaft, on which the cams for the intake and exhaust liftings of the valves are provided simultaneously, it is not possible to control the time point of the opening or closing of the intake valve independently of the time point of the opening or closing of the exhaust valve. Used in a known way for shifting the opening time points between intake and exhaust valves is a phase shifter, the cam geometries for the intake and exhaust valve stroke being provided on different camshafts. The intake camshaft is then shifted relative to the exhaust camshaft for the phase shifting.
Known from DE 103 14 683 A1 is a variable valve stroke control for an internal combustion engine having an underhead camshaft, in which the valve stroke of one or more intake and/or exhaust valves can be adjusted depending on load and rpm, so that, simultaneously with the valve stroke, also the opening time of the valves is adjusted. Known further from DE 100 41 466 A1 and DE 43 30 913 A1 are valve trains for controlling the intake and exhaust control timings of gas exchange valves and of the fuel intake control for an internal combustion engine. In both systems, however, a great effort must be put into keeping the valve play within a certain tolerance. Known, furthermore, are numerous variable valve trains that can adjust both the valve stroke and the opening time of the valve nearly continuously. All described variable valve trains utilize at least one variably adjustable transmission member to transmit the cam stroke by way of this transmission member to a valve actuating member, which produces the valve stroke. All of these systems are capable of producing a high variability of the valve stroke. However, most of these valve trains are described for overhead camshafts. Described in DE 101 40 635 A1 is a valve stroke mechanism for independent variable stroke adjustment of the gas exchange valves of an internal combustion engine, in which the valve stroke characteristic is created by the geometry of the slide gate path, by the contour of the adjusting strip, and by an operating curve of the rocker arm, so that the two intake valves of a 4-valve engine having different stroke curves are actuated by this stroke mechanism. Known from DE 1 751 690 and DE 2 256 091 are valve control units that, depending on the load and rpm, can change the valve stroke of a valve for internal combustion engines with an underhead camshaft. However, both of these are based on sliding contacts and accordingly result in problems entailing friction and thus power loss.
A drawback of the known mechanical variable valve trains having an underhead camshaft or rocker arms is that these valve trains use an additional lever, which transmits the movement of the push rod onto the intermediate member, which is responsible for the variability of the valve stroke curves. This thus results, for the same functionality, in more components and joint or contact sites. This further leads to greater problems in terms of tolerance as well as stiffness. In addition, the number of components and joint or contact sites has negative consequences for the system costs. A shifting of the control timing or a phase shifting of the maximum valve stroke is not provided for in this system. For the known systems described here, both the valve stroke and the valve opening time as well as the control timing or the phase position of the stroke maximum cannot be changed, even though the described systems are able to fulfill individual requirements placed on a mechanically variable valve train. However, there does not exist any system that can shift both the opening time and the stroke as well as the spread angle of the valves. Moreover, for an engine with only one camshaft, these systems do not provide for the possibility of adjusting separately the valve stroke parameters for the intake and exhaust valves.
Therefore, the problem of the present invention consists in creating a valve train for an internal combustion engine having an underhead camshaft or rocker arms with variable valve stroke and variable opening and closing times, making it possible to achieve a very compact transmission gear between the push rod drive or control shaft and the intake and exhaust valves, to reduce the number of components required for the transmission gear, and, in addition, to obtain a mechanical, completely variable valve train having an expanded variability of the valve train, particularly for engines with push rod or rocker arm trains.